1. Field of the Invention
The invention relates to a display device. In particular, the invention relates to a display device having a correction circuit for correcting a phase shift due to a delay of a signal which is input into a wiring. Further, the invention relates to an electronic device including the display device in a display portion.
2. Description of the Related Art
In recent years, a display device in which a semiconductor thin film is formed over an insulator such as a glass substrate, particularly, an active matrix display device using TFTs (Thin Film Transistors) has been widely used. The active matrix display device using TFTs includes hundreds of thousand of TFTs to millions of TFTs in pixel portions which are arranged in matrix, and lighting or non-lighting of each pixel is controlled to display an image.
In such a display device, a TFT is arranged in each pixel and lighting or non-lighting of each pixel is controlled by controlling on/off of the TFT.
In the aforementioned display device, an analog driving method (an analog gray scale method) and a digital driving method (a digital gray scale method) are given as examples of driving methods in the case of displaying a multi-gray scale image.
The analog driving method is a method for continuously controlling the amount of current which is supplied to a light-emitting element to obtain a gray scale. In addition, the digital driving method is a method for driving with only two states of an on state (a lighting state) and an off state (a non-lighting state) of a light-emitting element.
Since the digital driving method can only display two gray scales by itself, combination of the above method and a driving method which displays a multi-gray scale such as an area gray scale method, or combination of the above method and a driving method which displays a multi-gray scale such as a time gray scale method, has been proposed. The area gray scale method is a method in which a subpixel is provided in a pixel and a gray scale is displayed in accordance with a size of a light-emitting area in the subpixel. In addition, the time gray scale method is a driving method for controlling length of period in which a pixel emits light or the number of light emission to display a multi-gray scale. These driving methods are specifically disclosed in Reference 1: Japanese Published Patent Application No. 2001-5426 and Reference 2: Japanese Published Patent Application No. 2001-343933.